1. Field
This patent specification relates generally to an image forming method and apparatus with toner recycling unit, and more specifically to the method and apparatus provided with improved toner recycling capability by means of selectively switching between recycling and non-recycling modes based on the results from toner measurements in recycled toner.
2. Discussion of the Background
The electrophotographic image forming process is well known. In image forming apparatuses such as a copying machine, printer and facsimile apparatus, in general, the formation of the images is carried out through the electrophotographic steps of forming electrostatic latent images on an image bearing member, developing as visible toner images using toner particles, and transferring the toner images by a transfer means onto a copy sheet, which subsequently passes through a fixing unit to form fixed images on the sheet.
Following transfer of the toner images onto the copy sheets, residual developing material remaining on the image bearing member (or photoreceptor drum) is generally removed by a cleaning device such as, for example, cleaning blade, and subsequently collected in a container tank for containing recovered toner material.
During the formation of images on the image bearing member such as photoreceptor drum and also toner transfer onto a copy sheet by means of the transfer means, residual toner will generally result onto the image bearing member primarily for the following reasons: The rate of toner transfer during transfer steps is not able to reach 100% and the background density between images can not be zero, either.
The residual toner, therefore, results in the dirty background in contrast to produced images on copy sheets. As mentioned above, the residual toner is subsequently collected in a container tank to be discarded afterward.
With increasing concern for resources and operation costs in recent years, recycling of the used toner material has been devised. For example, there disclosed in Japanese Laid-Open Patent Application No. 6-175488 is that used toner is collected and returned by a toner transporting unit to several units such as developing unit and toner supplying unit to be admixed with fresh toner material, and is subsequently reused for forming toner images on the image bearing member. The recent trend for toner recycling continue to increase in conventional image forming apparatuses.
In addition, it may be noted that the ratio of the amount of residual toner material to the total amount thereof generally used in conventional image forming apparatuses ranges approximately from 15% to 25%.
Several foreign materials or contaminants, which are exemplified by paper dusts and toner aggregates with its size larger than the desirable size, are often included in recycled toner in no small numbers. These materials may be utilized repeatedly during the recycling process in the toner recycling unit incorporated in image forming apparatus. As a result, several drawbacks are encountered in the image forming using the recycling unit, which are known as picture image anomalies such as blank spots and dark dots.
Although there provided in the aforementioned disclosure is a filter unit for removing paper dusts and toner aggregates, satisfactory devices and techniques therefor are yet to be devised.
As one of the above-mentioned picture image anomalies, whisker images are cited, which are formed being whisker-shaped against white background on a copy sheet, as illustrated in FIG. 13.
The whisker images are considered to be caused by paper dusts. Namely, the paper dusts are first originated from copy sheets, contained in recycled portion of the toner, and transported to the image bearing member when recycled. Along the recycling steps, therefore, the concentration of the paper dusts steadily increases in recycled toner component in the recycling path.
During subsequent developing step with toner particles, toner particles are adhered to the paper dusts, and then displaced altogether onto the image bearing member. As a result, the thus formed paper dusts accompanied by toner particles are subsequently transferred onto a copy sheet during the transfer step, then emerge as the whisker images especially visible against white background of the copy sheet.
It is noted that the steady increase in the content of paper dusts in recycled toner is considered due to the fact that the portion of the paper dusts, which is previously formed in the developing unit and included in the recycled toner, is generally removed by a copy sheet, to thereby return to the developer along the recycling, and this portion is added to that of paper dusts originated now from newly fed copy sheets.
In case when a transfer unit is used incorporating another device such as transfer belt or roller, residual toner is also formed in these devices. However, this portion of residual toner is not recycled in practice, since the amount thereof is small and its quality is relatively poor because of a larger content of paper dusts than that remaining on the image bearing member.
In addition, the present inventors investigated in detail on the generation of paper dusts by experimentation. They have found the amount of paper dusts, which is transported to the image bearing member by each copy sheet, varies considerably depending on the kind, or the quality of copy sheet.
For example, paper dusts are rarely found in the residual toner for copy sheets of fine quality even after feeding 300 k (i.e., 300 thousand) copy sheets, which is in contrast with a larger amount of the paper dusts for recycled or ordinary papers, in that more than 50 whisker images are sometimes recognized on an A4 size sheet after 300 k copy sheets.
In order to alleviate such difficulties, an appropriate device such as, for example, a classifier may preferably be provided for removing aggregated toner particles and paper dusts. This is exemplified by a mesh mounted in a toner recycling path, in which toner particles that pass through the mesh are put into a recycled use, while those left out are discarded. In such a classifier, however, difficulties still persist such as in clogging by the particles, durability of the mesh, and thorough removal of residual particle or dusts on the mesh. Therefore, improvements are yet to be made on this technique as well.
In known image forming apparatuses incorporating toner recycling units, therefore, several difficulties are encountered of appropriately removing undesirable contaminants to thereby prevent picture image anomalies such as whisker images and dark dots, as mentioned earlier.
In addition, since the amount of paper dusts and toner aggregates, which are included in the recycled toner, varies considerably depending on the kind of copy sheet and of toner in use as also indicated above, another method may be devised, in which the amount of the toner to be recycled out of the recovered toner is suitably adjusted depending on the above-mentioned amount of the contaminants which is presently obtained. That is, the ratio of the amount of recycled toner to that of recovered toner, or toner recycling rate, is adjusted so as to prevent picture anomalies.
However, since the amount of contaminants further varies depending on temperature and humidity as well, precise estimation and subsequent adjustments of the toner recycling rate has remained quite difficult in practice. This difficulty may therefore cause another problem, in that some of recovered toner may be wastefully discarded when the recycling system is operated with unduly low toner recycling rate.
Accordingly, it is an object of the present disclosure to provide an image forming apparatus provided with an improved toner recycling unit, having most, if not all, of the advantages and features of similar employed units, while eliminating many of their disadvantages.
It is another object of the present disclosure to provide a toner recycling unit in the image forming apparatus capable of efficiently recycling the toner recovered from a cleaning unit, which is devised such that the selectable switching between the toner recycling and non-recycling modes be continually carried out according to the decision based on the present amount of paper dusts, thereby preventing the emergence of undesirable picture image anomalies.
The following brief description is a synopsis of only selected features and attributes of the present disclosure. A more complete description thereof is found below in the section entitled xe2x80x9cDescription of the Preferred Embodimentsxe2x80x9d
An image forming method is disclosed herein including at least the steps of forming an electrostatic latent image on an image bearing member, forming a toner image by developing the latent image using toner on the image bearing member, transferring the toner image to a substrate, and recovering the toner material remaining on the image bearing member following the transfer.
This image forming method is characterized by including the following additional steps such as
computing an acceptable number of count of copy sheets that can be utilized in image forming in the forthcoming series of copying steps until immediately before the threshold for the emergence of picture image anomalies caused by contaminants in the toner in the toner recycling unit, based on a prescribed number of count of copy sheets that is experimentally obtained in advance, under a variety of mutually independent conditions, as the number of count of copy sheets that can be utilized in image forming for the period of time from the start of the recycled use of the toner until immediately before the threshold for the emergence of picture image anomalies caused by contaminants in the toner in the toner recycling unit, and on a cumulative sheet count which is accumulated in the present series of copying steps under running conditions as the number of count of copy sheets that is accumulated in the present series of copying steps after starting the recycled use of the toner, in which,
if the acceptable number of count of copy sheets is equal to, or greater than an anticipated number of count of copy sheets that can be utilized in image forming in the forthcoming series of copying steps, the forthcoming series of copying steps are carried out in the toner recycling mode,
while the acceptable number of count of copy sheets is less than an anticipated number of count of copy sheets that can be utilized in image forming in the forthcoming series of copying steps, the forthcoming series of copying steps are carried out in the toner non-recycling mode.
In addition, at the instant when the acceptable number of count of copy sheets is exceeded by the anticipated number of count of copy sheets, a toner discarding mode is implemented, in which all of the toner, that is recovered by the cleaning unit to be recycled into the developing unit, is discarded to a toner discarding tank.
Accordingly, it becomes feasible with the present method of image forming for the toner recovered by the cleaning unit be efficiently recycled without removing contaminants such as aggregated toner particles and paper dusts included in the recycled toner.
In addition, since contaminants of the amount unduly large, which may cause whisker images, can be excluded from the toner recycling path, the occurrence of undesirable picture image anomalies can be prevented.
According to another aspect, an image forming apparatus is disclosed including at least an image bearing member, an exposure unit for forming an electrostatic latent image on the image bearing member, a developing unit for forming a toner image by developing the latent image using toner on the image bearing member, a transfer unit for transferring the toner image to a substrate, a cleaning unit for cleaning the image bearing member by removing the toner material remaining on the image bearing member following the transfer, and a toner recycling unit for returning the toner removed from the image bearing member to the developing unit.
This image forming apparatus is characterized by including the following additional units such as
a prescribed sheet count memory for storing a prescribed number of count of copy sheets that is experimentally obtained as the count that can be utilized in image forming for the period of time from the start of the recycled use of the toner until immediately before the threshold for the emergence of picture image anomalies caused by contaminants in the toner in the toner recycling unit,
a cumulative sheet count memory for storing a cumulative number of count of copy sheets that is accumulated in the present series of copying steps after starting the recycled use of said toner,
a computing unit for computing an acceptable number of count of copy sheets that can be utilized in image forming in the forthcoming series of copying steps until immediately before the threshold for the emergence of picture image anomalies caused by contaminants in the toner in the toner recycling unit, based on the acceptable number of count of copy sheets, and the prescribed number of count of copy sheets stored in the prescribed sheet count memory and a cumulative sheet count memory, respectively, and
a selection unit for selectably switching between toner cycling mode and toner non-cycling mode for the image forming apparatus, based on the acceptable number of count of copy sheets computed by the computing unit.
In addition, this image forming apparatus may further includes a toner recycling path unit for transporting the toner removed from the image bearing member to the developing unit, a toner discarding path unit for transporting portions of the toner removed by the cleaning unit to a toner discarding tank, and a toner path switching unit for selectably switching between the toner recycling path unit and toner discarding path unit, based on the acceptable number of count of copy sheets computed by the computing unit, in which, at the instant when the acceptable number of count of copy sheets is exceeded by the anticipated number of count of copy sheets, the toner path switching unit is instructed to implement the toner discarding mode, in which all of the toner, that is recovered by the cleaning unit to be recycled into the developing unit, is discarded into a toner discarding tank.
It is noted that the prescribed number of count of copy sheets is the number experimentally obtained in advance, under a variety of mutually independent conditions, as the number of count of copy sheets which can be utilized in image forming for the period of time from the start of the recycled use of the toner until immediately before the threshold for the emergence of picture image anomalies caused by contaminants in the toner in the toner recycling unit, and that the cumulative sheet count is the number accumulated in the present series of copying steps under running conditions as the number of count of copy sheets which is accumulated in the present series of copying steps after starting the recycled use of said toner, in which the computing unit is adapted to compute the acceptable number of count of copy sheets which can be utilized in image forming in the forthcoming series of copying steps under running conditions until immediately before the threshold for the emergence of picture image anomalies caused by contaminants in the toner in the toner recycling unit.
Accordingly, it becomes feasible with the present construction of the image forming apparatus for the toner recovered by the cleaning unit be efficiently recycled without removing contaminants such as aggregated toner particles and paper dusts included in the recycled toner, to thereby the emergence of undesirable picture image anomalies be effectively prevented.
According to still another aspect, an image forming apparatus is disclosed including at least an image bearing member, an exposure unit for forming an electrostatic latent image on the image bearing member, a developing unit for forming a toner image by developing the latent image using toner on the image bearing member, a transfer unit for transferring the toner image to a substrate, a cleaning unit for cleaning the image bearing member by removing the toner material remaining on the image bearing member following the transfer, and a toner recycling unit for returning the toner removed from the image bearing member to the developing unit.
This image forming apparatus is characterized by including the following additional units such as
a paper dust measuring unit provided in a paper dust removal unit for measuring the amount of paper dusts collected in the paper dust removal unit, which are adhered to, and subsequently removed from, feeding rolls,
a dust amount estimating unit for estimating the amount of paper dusts included in the toner recovered by the cleaning unit based on the results from the estimation by the dust amount estimating unit, and
a computing unit for computing the acceptable number of count of copy sheets that can be utilized in image forming in the forthcoming series of copying steps for the period of time from start of the recycled use of the toner until immediately before the threshold for the emergence of picture image anomalies caused by contaminants in the toner in the toner recycling unit, based on the results on the amount of paper dusts from the estimation by the dust amount estimating unit, and
a selection unit for selectably switching between toner cycling mode and toner non-cycling mode for the image forming apparatus, based on the acceptable number of count of copy sheets computed by the computing unit.
Accordingly, it becomes feasible with the present construction of the image forming apparatus for the toner recovered by the cleaning unit be efficiently recycled without removing contaminants such as paper dusts and toner aggregates included in the recycled toner, thereby eliminating undesirable picture image anomalies.
The present disclosure and features and advantages thereof will be more readily apparent from the following detailed description and appended claims when taken with drawings.